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Arsenate Removal from Synthetic Groundwater by Coagulation with in Situ Formed Fe(¢ó) and Mechanism S

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Tutor: GuanXiaoHong
School: Harbin Institute of Technology
Course: Municipal Engineering
Keywords: In-situ formed Fe(¢ó),FeCl3,As(¢õ),coagulation,hydrolysis
CLC: TU991.2
Type: Master's thesis
Year:  2012
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Abstract:
Arsenic was ubiquitous in the earth¡¯s crust. It was widely found in soil, sediment, natural water, air and living organisms. Arsenic usually entered the body through the respiratory system, digestive system or skin triggering a series of acute or chronic symptoms. With the intensification of human activities, the balance of arsenic in the natural environment was interrupted and had a tendency to increase its concentration and distribution on a global scale.Common methods for arsenic removal involved biological method, adsorption, ion exchange, membrane and co-precipitation. Arsenic removal by Ferric salt coagulation attracted lots of attention for its economic, stable and efficient features t But arsenic remval by coventional iron salt coagulation always led to abounded and corruption of water treatment structures.This paper systematically investigated the performance and coagulation behavior of in-situ formed Fe(¢ó) and ferric chloride coagulation process on arsenate removal under different operating conditions.and ecology of iron and ferric chloridethe Hydrolysis product of the processes were also characterization by AFM, XRD and FTIR¡£Arsnate removal efficity declined with an increasing of pH levels in all of the three processes.In-stu formed Fe(¢ó) processes had an advantage of7-23%compare to Ferric coagulation process.The best oxidant/Fe(¢ò) was H2O2/FeCl2=1:2, KMnO4/FeCl2=1:3respectively.The advantage was more obvious at moderly acidic condition or low cogualant dosage or high initial As(¢õ) concerntration.Suprisingly, FeCl2-H2O2was more effective than FeCl2-KMnO4.The three processes could achieve MCL(10¦Ìg L-1) seted by elevating coagulat dosage and In-situ formed Fe(¢ó) and FeCl3required4,8mg L-1coagulant respectively to degraded initial1mg L-1As(¢õ) to MCLThe growth stage of flos in various processes can be divided into two phases namely rapid growth stage and stable stage. The growth rate and sizer of flocs was in following order,FeCl3> FeCl2-KMn04> FeCl2-H2O2.Flocs broken at slow mixing stage aided arsenate removal in the various processes especially for FeCl3process or at pH=6,7or broken at early stage. On one hand,Flocs broken speeded up the process of mass transfer, on the other hand it maked the floc inner face fully exposed to fully play its arsenic removal performance. The oxidant secondary dosing in in-situ formed Fe(¢ó) processes promoted arsenate removal and it further illustrated the importance of floc formation and growth rate in arsenate removal process.Zeta potential data demonstrated charge neutralization played no role in arsenate removal.At pH=6-8, rapid oxidation of Fe (¢ò) was rapidly oxidized when dosing in in-situ formed Fe(¢ó) processes. Content of Fea were in a range of2.5-3.7%, but Feb varied in the following order, FeCl2-KMnO4> FeCl2-H2O2> FeCl3, and abundant Feb generated in in-situ formed Fe(¢ó) processes accounted for the advantage to some degree¡£Micromorphology of flocs varied. The surface of flocs from FeCl2-KMnO4process undulated gently and was rough and cotton-look. The surface of floes from FeCl3took the shape of dice and was smooth. The surface of flocs from FeCl2-H2O2was rough but flat. XRD data demonstrated amorphous or quasi-crystal morphologyFTIR showed (FeO) AsO3-formed in varios processed at pH=7.
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